Amino methylated or Mannich (alk)acrylamide polymers in inverse (water-in-oil) microemulsion form are used as flocculants for separating suspended material from aqueous dispersions. As such, they are preferred over other types of flocculants because of their high solids content, low bulk viscosity, their tendency to reduce interpolymer crosslinking problems, and superior performance. These inverse microemulsion Mannich acrylamide polymers (microemulsion Mannich PAMS) are described in U.S. Pat. Nos. 4,956,399; 4,956,400; 5,037,863; 5,132,023 and 5,037,881, which are incorporated herein by reference. Oftentimes, these Mannich acrylamide polymers are quaternized and used in their highly charged cationic state. It has been found, however, that for certain flocculant applications, the cationic charge on the microemulsion Mannich PAMS may be too high and may inhibit the performance of the polymeric flocculant. For example, many aqueous dispersions containing paper deinking sludge or other suspended material resulting from the processing of recycled paper have relatively low cationic demand. Consequently, highly cationized quaternary microemulsion Mannich PAMS have not performed as efficiently as desired in these flocculation applications. Ampholytic polymers have been found to be a viable alternative.
Ampholytic polymers in emulsion form are known to be useful for treating sewage and industrial wastes as disclosed in U.S. Pat. Nos. 4,330,450 and 4,363,886. But these polymeric emulsions do not provide the benefits of microemulsions, (e.g. higher solids and reduced crosslinking). Furthermore, the amount of anionic comonomer sufficient to provide a polymer with a standard viscosity of at least 2.1 cps for effective treatment of sludge having a relatively low cationic demand is also not provided.
Japanese patent application No. 63-218246 discloses a polymeric water-in-oil emulsion having anionic and cationic properties which is made by mixing an anionic polymeric inverse emulsion having 5 to 100 mole percent anionicity with a cationic polymeric inverse emulsion having 5 to 100 mole percent cationization. This system does not, however, provide ampholytic properties, due to charge neutralization, since the charges result from a mixture of two differently charged polymers as opposed to a single ampholytic polymer.
Compositions comprising crosslinked anionic or amphoteric polymeric microparticles, as taught in U.S. Pat. No. 5,171,808, may be used for facilitating the solid-liquid separation of various biologically treated suspensions but such polymeric microparticles only have solution viscosities of at least 1.1 mPa.s and may not flocculate as well as desired.
While ethylenically unsaturated anionic comonomers have been incorporated into microemulsion Mannich PAMs, see e.g., U.S. Pat. No. 4,956,400 and U.S. patent application No. 07/860,542 filed on Mar. 30, 1992, and incorporated into Mannich PAMs, see e.g., U.S. Pat. No. 4,137,164, the effective amount of anionic comonomer cannot be ascertained from these patents and not all of the resulting anionic copolymers disclosed in the patents are particularly effective in treating aqueous dispersions having a low cationic demand or high total solids. Even if one were to quaternize the resulting anionic copolymers to provide ampholytic copolymers, the resulting ampholytic copolymers would also be ineffective for treating aqueous dispersions, particularly those having low cationic demand and/or high total solids.
There exists a need for polymeric flocculant that can be prepared at high polymer solids levels and can perform effectively in treating aqueous dispersions especially those having a low cationic demand or high total solids. It has now been found that copolymers of quaternary aminomethyl (alk)acrylamide and about 1 to about 15 mole percent of at least one ethylenically unsaturated anionic comonomer wherein such copolymers have a standard viscosity of at least 2.1 cps provide superior flocculating performance relative to microemulsion Mannich PAMS and other flocculant agents in the art with respect to certain aqueous dispersions containing suspended materials. While these polymers provide the benefits of microemulsion Mannich PAMS, such as low bulk viscosity and high solids content, and may be used like the known Mannich PAM microemulsions in various flocculation applications, the ampholytic polymers of the present invention also tend to be more effective in flocculating aqueous dispersions which don't flocculate well using highly cationically charged polymers, i.e., aqueous dispersions such as sludges which have a somewhat lower cationic demand.
Therefore the present invention provides ampholytic polymers or copolymers of quaternized dialkylaminomethylated (alk)acrylamide and anionic comonomer which provide all of the benefits of microemulsion Mannich PAMS yet also tend to be more effective than current cationic flocculants in treating suspended solids in aqueous dispersions having somewhat lower cationic demands and sludges having total solids levels of at least about 4 weight percent.
The present invention also provides a process for preparing an ampholytic copolymer and an inverse microemulsion ("microemulsion" herein) comprising an ampholytic copolymer of quaternary dialkylaminomethyl (alk)acrylamide and ethylenically unsaturated anionic comonomer having a standard viscosity of at least 2.1 cps. Methods of using these ampholytic polymers to flocculate suspended material in various aqueous dispersions such as deinking process waters resulting from the processing of recycled paper and various sludge-containing dispersions are also encompassed within the present invention.